Due to rapid growth in use and applications of digital information technology, there are demands to continuingly increase the memory density of memory devices while maintaining, if not reducing, the size of the devices. Three-dimensional (3D) structures have been investigated for increasing the memory density of a device. For example, 3D cross-point memory cells and 3D-NAND cells have been investigated as devices with increased capacity and smaller critical dimensions. Typically, these 3D structures include stacks of memory cells that may include phase change materials, switching diodes, charge storage structures (e.g., floating gates, charge traps, tunneling dielectrics), a stack of alternating control gates and dielectric materials, and charge blocking materials between the charge storage structures and adjacent control gates.
Fabrication of conventional semiconductor devices often requires creating high aspect ratio openings in a stack of alternating materials on a substrate. Frequently, materials that are highly sensitive to downstream processing conditions are used as part of the stack structures. For example, stacks in 3D memory arrays may comprise materials such as chalcogenides, carbon containing electrodes, or other sensitive materials that may be damaged at higher temperatures used during conventional semiconductor fabrication processes or may react with etchants used during downstream processing. Aluminum oxide has been used as a liner material to protect the sensitive materials of the stack structures. However, aluminum oxide may resputter and redeposit on surfaces of a semiconductor structure during etching. As the aluminum oxide resputters, it may undesirably form in bottom portions or corners of trench structures or undesirably redeposit on other portions of the semiconductor structure. Additionally, removing the aluminum oxide without damaging the sensitive materials of the stack structures has proven to be difficult. Aluminum oxide exhibits high dry etch resistance to CFx based dry etch chemistries and O2-plasma based carbon etch chemistries.
In addition, as the number of materials in the stacks increase, the depth and aspect ratio (i.e., the ratio of width to depth) of trenches located between adjacent stack structures increases. It is important to constrain the critical dimension of the structure as the trenches are formed. Therefore, it would be desirable to form high aspect ratio trenches between stack structures in a device having a 3D architecture without increasing the critical dimension of the structure.